This invention relates to a crimp terminal for an aluminum wire and a method of producing the crimp terminal, and more particularly to an improved technique of increasing an area of adhesion of the crimp terminal to the aluminum wire.
A conventional crimp terminal is formed by pressing a single metal sheet into a predetermined shape, and therefore has an integral or one-piece construction, and includes a conductor press-fastening portion 500 formed at a rear end portion of a terminal body portion thereof. As shown in FIG. 7, the conductor press-fastening portion 500 is adapted to be crimpingly connected to that portion of a wire conductor 505 of a sheathed wire 501 exposed by removing an insulative sheath 503 from the sheathed wire 501. The conductor press-fastening portion 500 includes a bottom plate portion 507 for the placing of the wire conductor 505 thereon, and a pair of press-fastening claws 509 extending respectively from opposite side edges of the bottom plate portion 507 so as to be press-fastened (or crimped) onto the wire conductor 505 placed on the bottom plate portion 507.
In order to enhance both an electrical connection and a mechanical connection between the wire conductor 505 and the bottom plate portion 507 of the crimp terminal, it is known that a plurality of conductor retaining grooves (hereinafter referred to as “serrations”) 511 of a generally channel-shaped cross-section are formed in an inner surface 507a of the bottom plate portion 507 for contact with the wire conductor 505, and extend in a direction intersecting (usually, perpendicular to) an axis G of the wire conductor 505. In the case of crimping the crimp terminal to a copper wire, groove edges 511a of the serrations 511 are pressed hard against the surface of the wire conductor 505 to suitably bite thereinto upon press-fastening of the press-fastening claws 509, and by doing so, both the mechanical connection performance and the electrical connection performance can be enhanced, thus ensuring the reliability of the connection by press-fastening.
[Patent Literature 1] JP-A-2003-31274
In recent years, aluminum wires each comprising a wire conductor 505 made of aluminum have been extensively used for the purpose of achieving a lightweight design of the wire. Particularly when such aluminum wires are used in a wire harness for installation on a vehicle, the aluminum wires are effective in improving fuel consumption and an acceleration performance since the overall weight of the wire harness can be reduced.
However, in the case of crimping the crimp terminal to the aluminum wire, it is necessary to effect hard crimping in order to stabilize the electrical performance, and it has been difficult to balance the electrical performance with the mechanical performance. In order that when the edges 511a of the serrations 511 bite into the wire conductor 505, an oxide film formed by oxidation on the surface of the wire conductor 505 can be removed by the edges 511a, it is necessary to set the amount of biting to a relative large value. In order to increase the biting amount, it is necessary to increase a depth d of the serrations 511. On the other hand, in the case were the biting amount is set to such a large value, stresses concentrate on the press-fastened portion of the wire conductor 505 when an external pulling force acts on the wire conductor 505. Therefore, particularly in the case of the aluminum wire, the wire conductor 505 is liable to be cut or severed, and consequently the mechanical connection performance is lowered. And besides, it is difficult to secure the strength of the terminal which can withstand hard crimping.